Semiconductor device packages or integrated circuit chip carriers find use in a variety of high-density electronics applications. The integrated circuits or semiconductor devices are typically protected from the external environment by transfer molding a thermoset or thermoplastic resin about the device. This package provides protection from dust, humidity and other environmental factors which can destroy the delicate circuitry.
A major problem associated with these types of packages is that they do not provide shielding from radiation, such as radio frequency interference (RFI) or electromagnetic interference (EMI). This ability to shield high-frequency circuits, especially in electronic equipment such as two-way radios, is critical. Conventional shielding systems are generally characterized by a conductive metallic enclosure constructed to surround the device to be shielded. This enclosure acts either to protect the electrical equipment from external RFI or EMI signals or to prevent the escape of RFI or EMI signals generated by the device. Typically, these shielded enclosures are made from a conductive material that is electrically coupled to the surrounding area. In prior art, the shielded enclosures have been made by attaching a drawn metallic casing over the transfer molded package and soldering the metal casing to a substrate connected to the device.
Unfortunately, this method of shielding is extremely sensitive and very costly and cumbersome when used to shield integrated circuits because 1) high temperatures generated during the soldering process for attaching the metal shield to the device, 2) the additional thickness or bulk required when adding a shield, and 3) the additional cost associated with the soldering operation.
Heat generated by the soldering process may be conducted directly to the integrated circuit and can result in damage to the circuit. In order to minimize the damage caused by the soldering operation, due care is required to control the soldering process in order to prevent jeopardizing the quality of the integrated circuit. The increase in the overall size of the shielded package is substantial, due to the additional thickness of the shield. This thickness results in a package that is larger than optimum. The step of soldering the shield also requires additional assembly time and labor, adding further cost to the final package. Providing shielding for integrated circuits in this way requires special mounting and holding fixtures for the shield and the integrated circuit package.
As a result, a need exists for a method to provide RFI shielding to a high-density integrated circuit package that is economical, does not generate excessive temperatures, and provides a low-profile, high-density package.